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Distortion control of cutting piece in CNC plasma cutting machine

CNC plasma cutting machine with multi-function, high efficiency, high-speed, high precision, low labor intensity and high degree of automation, suitable for processing many varieties, small batch, complex shape, exchange frequent parts, widely used in automobiles, locomotives, , Chemical machinery, nuclear industry, general machinery, engineering machinery, steel structure and other industries. CNC plasma cutting can cut oxygen difficult to cut a variety of metal materials (using plasma arc can also cut some non-metallic materials), its main advantages are: cutting the thickness of the ordinary carbon steel sheet, the cutting speed up to oxygen cutting The cutting surface is smooth, the thermal deformation is small, the incision width and the cutting face angle are large, the special cutting cutting torch or process can be used to cut the thin plate to get close to the vertical cutting surface and so on [1]. CNC plasma cutting machine cutting quality of the processing of the entire product plays a key role, it is effective to prevent the deformation of the workpiece is particularly important.


1 thermal deformation of cutting parts and the causes

Any object under external force can cause changes in shape or size, this phenomenon is called deformation. Deformation includes elastic deformation and plastic deformation. After the removal of external force, can restore the original size, shape, known as elastic deformation, and the formation of permanent deformation known as plastic deformation. During the cutting of the sheet metal, the cutting member is plastically deformed until it is cooled to the initial temperature, which is called final heat deformation. Plasma cutting is the use of high-energy density plasma arc and high-speed plasma flow, the molten metal blown away from the cut to form a continuous cut to achieve the purpose of separation of metal plates [1]. Although the thermal deformation of plasma cutting is small, but the sheet metal in the rolling, cooling process, there is unavoidable residual stress. Cutting, the metal by the impact of local high-temperature heat source in the direction of rapid expansion of the cutting direction, and around the parent metal and limit its expansion, the edge of the metal to produce stress, when the stress exceeds the metal yield strength, will produce plastic deformation, with cooling It will shrink, cooling to room temperature, due to the surrounding base metal limit, along the cutting direction will have a certain degree of shortening deformation, while there is a certain residual tensile stress, which is produced cutting deformation of the reason.


2 choice of cutting process

In order to minimize the cutting deformation, cutting must ensure that the accurate positioning of metal plate reliable, where conditions permit, the use of multi-point contact electromagnetic platform for proper leveling, in order to eliminate the uneven residual stress of metal sheet, Improve plate flatness. CNC plasma cutting machine is the use of high-speed, high temperature, high-energy plasma cutting machine and computer control to combine the cutting sheet metal equipment. Its working process is in accordance with the pre-programmed procedures for automatic control, and identify the processing procedures, so before the choice of a reasonable cutting process 11 cutting the starting point, direction, sequence, speed, cutting quality of the processing Plays a decisive role.


2.1 arc from the point of choice

In general, the cutting point of the starting point of the metal plate in the edge, or cut in the workpiece has been cutting the middle of the most ideal. When the distance is too large, there is no arc or broken arc, so that the workpiece is not cut through, resulting in waste or scrap; when the distance is too small, easy to short-circuit between the nozzle and burn the nozzle, damage the normal cutting process. Practice has proved: the nozzle from the workpiece height is generally 6 ~ S mm is appropriate, air plasma cutting and water re-compression plasma arc cutting nozzle height of the workpiece can be slightly less than 6 ~ S mm.


2.2 The choice of cutting direction

The correct cutting direction should be to ensure that the final cutting edge and the motherboard most of the detachment, if prematurely with the motherboard most of the detachment, the surrounding corner box is insufficient resistance to the cutting process of thermal deformation stress, resulting in cutting parts Cutting process shift, there is size tolerance [2].


2.3 The impact of the cutting sequence

The cutting sequence is the order in which a nested row of nested parts of a steel plate are sequentially cut. Generally should follow the principle of "first after the first, after the first small": that is, first cutting the workpiece within the contour (or within the outline of the nested parts), after cutting the outer contour; first cutting area of small parts, after cutting Large-size parts, otherwise, in the metal plate cutting internal contours or other small parts will be deformed, resulting in scrap pieces of processing.


2.4 Cutting speed selection

Cutting speed is cutting the process of cutting torch and the relative speed of movement between the workpiece, the appropriate cutting speed is an important condition for the straight surface of the incision. Cutting speed depends on material thickness, cutting current, gas type and flow, nozzle structure and the appropriate amount of post-tug and so on. Increasing the cutting speed at the same power will cause the incision to be skewed. Cutting torch should be perpendicular to the surface of the workpiece, but in order to facilitate the exclusion of slag, can be slightly with a certain inclination (generally less than 3), so in order to improve productivity, should ensure that cut through the premise May choose a large cutting speed.


3 Deformation analysis and control of cutting parts

Due to the thermal expansion and contraction of the sheet, the workpiece in the cutting process and the residual material will have a relative movement, according to the quality of the workpiece and the residual material quality difference, resulting in relative movement can be divided into the following three cases:(L) When the workpiece quality is much greater than the remaining material quality, the workpiece does not move, I material relative to the platform to move, does not affect the size of the workpiece. (2) When the workpiece quality is much less than the remaining material quality, the workpiece relative to the platform to move, I do not move, the workpiece to produce a certain deviation. (3) When the quality of the workpiece and the remaining material quality is equivalent, the workpiece and the remaining material relative to the platform may have moved to affect the size of the workpiece. Practice shows that the workpiece or residual material relative to the movement of the platform, the workpiece size error generated in general between O.3 ~ 4. O mm.


3.1 deformation of the workpiece unilateral control

In the numerical control plasma cutting process to select a reasonable cutting process, the resulting deformation is also different. If cutting the plate shown in Figure l, if the point A is the starting point, cutting direction and order of A! D! C! B! A, as shown in Figure la. When the AD segment cutting, processing DC segment, the DC segment more than expected narrow material, cutting the high temperature so that the DC segment more than linear elongation, CB segment outward deflection, after cutting the DC segment size reduction !, Figure lb As shown, the size of the DC is proportional to the size of the DC segment. If you choose A! B! C! D! A cutting sequence, the workpiece by the DA and the motherboard at the end of separation, can effectively reduce the cutting deformation.

3.2 deformation of elongated pieces of control

  For the cutting of the elongated member as shown in Fig. 2, the expansion of the BC segment prevents the expansion of the CD segment when the DA segment is cut by pressing A! B! C! D! A to complete the integral cut. After cooling, The amount of contraction is larger than the contraction of the BC segment, bending the workpiece toward the DA side. The size of the next bend depends on the aspect ratio of the workpiece Y! X, the greater the aspect ratio, the greater the amount of side bending.

If you use two workpiece pair cutting, as shown in Figure 3, if you choose A point for the starting point, cutting direction and order of A B! C! D! E! A! In the completion of the DE segment, with the mother board is equivalent to the workpiece aspect ratio reduced by half, so that the next bend amount! Reduced, when cutting AF segment, so that both sides of the workpiece expansion and contraction of the same, slender deformation Significantly reduced.

3.3 cutting of special-shaped pieces of technology

For the cutting of special shaped parts as shown in Fig. 4, the following cutting process can be selected.

(L) for the concave pieces to take two pairs of cutting method, the first cut inside, after cutting the outside, and finally from the outside to the inside to make two separate. Cutting the order shown in Figure 5, the inner edge: Al! Bl! Cl! Dl! Al; outside: A! B! C! D! A; cut off: E! F, H!

(2) for the bias hollow pieces should be taken two pairs of cutting, and finally make two separate. The cutting sequence is shown in Fig. 6, the inner edge: Al! Bl! Cl! Dl! Al, A2! B2! C2! D2! A2; Outer edge: A! B! C! D! A;

4 Conclusion

    CNC plasma cutting in the processing industry both in terms of cutting quality and cutting benefits are superior and flame cutting, it can be used with different working gases can cut a variety of metals, especially for non-ferrous metals (stainless steel, aluminum, copper, titanium, nickel, etc.) Cutting better. The paper analyzes the deformation law and influence of the cutting parts of the CNC plasma cutting machine, carries on the appropriate plate leveling treatment before the cutting, and reasonably fixes the plate to prevent the workpiece from moving during the cutting process. When selecting the cutting procedure, select a reasonable cutting process, So that the maximum size of the workpiece surface and the final separation of the mother board; for cutting elongated pieces or shaped pieces, the use of two pairs of cutting control methods such as cutting methods can effectively prevent or reduce the deformation of cutting parts.